Electrolytic process for the preparation of {60 -methylbenzyl dimers from sulfonium compounds

ABSTRACT

Alpha -Methylbenzyl dimers having the formula WHEREIN N IS AN INTEGER FROM 0 TO 5 AND R is an inert substituent, are prepared by electrochemically reducing a sulfonium salt having the formula WHEREIN R1 and R2 are alkyl or hydroxy-substituted alkyl groups and A is an electrolytically acceptable anion. The reduction and coupling occur at a mercury cathode without the formation of organomercury compounds.

United States Patent Settineri et al.

[54] ELECTROLYTIC PROCESS FOR THE PREPARATION OF a-METHYLBENZYL DIMERSFROM SULFONIUM COMPOUNDS [72] Inventors: William J. Settineri; RitchieA. Wessling,

both of Midland, Mich.

[73] Assignee: The Dow Chemical Company, Midland,

Mich.

22 Filed: Dec.2, 1969 21 Appl.No.: 881,574

52 us. (:1 ..204/72 51 lnt..Cl. ..C07b 29/06, C07c 1/00, C07c 15/1 2 58Field or Search .104/72, 73 56 References Cited UNITED STATES PATENTS3,480,527 11/1969 Wessling et a] .204/73 3,480,525 11/1969 Wessling eta]. ..2o4/59 Primary Examiner-F. C. Edmundson Attorney-Griswold &Burdick and C. E. Rehberg 1 51 May 2,i972

[57] ABSTRACT a-Methylhenzyl dimer5 having the formula -011c11- :113AJII; (R (R n wherein n is an integer from 0 to 5 and R is an inertsubstituent, are prepared by electrochemically reducing a sulfonium salthaving the formula eB/Rl @Am-rr A wherein R1 and R1 are alkyl orhydroxy-substituted alkyl groups and A is an electrolytically acceptableanion.

The reduction and coupling occur at a mercury cathode without theformation of organomercury compounds.

10 Claims, No Drawings ELECTROLYTIC PROCESS FOR THE PREPARATION OFa-METI-IYLBENZYL DIMERS FROM SULFONIUM COMPOUNDS BACKGROUND OF THEINVENTION Polarography is an extremely useful analytical method ofdetermining qualitatively and quantitatively the cations in a solution.The polarography of certain sulfonium compounds is described byColichman and Love, J. Org. Chem., 18, 40 (1953).

The preparation of p,p-dinitrobibenzyl by electrochemical reduction ofp-nitrobenzyl sulfonium compounds, e.g., pnitrobenzyldimethylsulfoniumchloride is described in U.S. Pat. No. 3,480,527. The reduction andcoupling reaction occurred using various cathodes and electrolysissolvents, e.g., a mercury cathode and an aqueous solution of thesulfonium salt. However, other benzyl sulfonium salts in an electrolytesolution reacted with a mercury cathode to form bisorganomercurycompounds, as described in our copending application, Ser. No. 881,573filed December 2, 1969 and entitled Process for ProducingBisorganomercury Compounds by the Electroreduction of SulfoniumCompounds. E.g., the electrolysis of an aqueous solution of benzylorp-isoamylbenzyldimethylsulfonium chloride using a mercury cathodeproduced in about 90 percent yield dibenzylmercury andbis(p-isoamylbenzyl)mercury, respectively.

The subject process, as well as the above processes, utilize sulfoniumsalts and an electrolysis system comprising an anode, a cathode, anelectrolysis solvent and a means for applying and maintaining anelectrical potential between said anode and cathode.

SUMMARY OF THE INVENTION It has now been discovered that a-methylbenzyldimers having the formula wherein n is an integer of from O to 5 and Ran inert, substantially non-interferring group, i.e., R is a group whichis inert in the process and which does not sterically hinder or preventthe formation of the desired product (such stearic considerations beinga factor when R is in the ortho ring positions) are produced in thenovel process comprising subjecting an amethylbenzyl sulfonium salt inan electrolysis solvent to an electrical potential sufficient to reducethe sulfonium salt; the sulfonium salt having the formula (II) R1wherein n and R have the above meaning and R and R are alkyl orhydroxy-substituted alkyl groups of from one to about l5 carbon atomsand A" is an electrolytically acceptable anion. The compounds thusproduced are useful as lubricants, as additives in extreme pressurelubricant compositions, as surfactants when R is a polyhydroxyalkylgroup, as reactants for making useful novolac and alkyd resins when R ishydroxy, hydroxyalkyl or hydroxyaryl, and other like uses which will beapparent to those skilled in the art.

The discovery that the electrolysis of a-methylbenzyl sulfonium salts,with or without stabilizing parasubstituents, produced thea-methylbenzyl dimers using a mercury cathode was most surprising inview of the results obtained by electrolysis of benzyl sulfonium saltsas set forth in our aboveidentified copending US. applications.

Suitable sulfonium salts in the subject process are represented by II inwhich suitable inert R groups include halogens, such as a fluoro, chloroor bromo; hydroxy; nitro; or hydrocarbon groups, such as alkyl, aryl,aralkyl, alkaryl, alke- 'nyl, cycloaliphatic, and the like, and haloorhydroxy-substituted such hydrocarbon groups of from one to about 25carbon atoms. The preferred sulfonium salts are those wherein (a) n isan integer of from O to 2, or (b) R, and R are alkyl orhydroxy-substituted alkyl of from 1 to about 4 carbon atoms; the mostpreferred sulfonium salts are those wherein n is 0 or I (particularlythe para-substituted reactants), R is alkyl or haloorhydroxy-substituted alkyl, and R and R are alkyl or hydroxy-substitutedalkyl of from one to about four carbon atoms. Representative examples ofsuitable sulfonium salts include those within ll having the formula(III) RI CH: R2

wherein:

TABLE I o-Substituent p-Suhstituent Toiylate (l Br Tosylatn Benzoate Fand other compounds, such as pentafluoro-a-methylbenzyldiethylsulfoniumchloride, m-nitro-a-methylbenzyldi-n-butylsulfonium nitrate,3,5-dimethyl-a-methylbenzyldioctylsulfonium bromide,3,5dihydroxya-methylbenzyldiisobutylsulfonium fluoride, and the like.

The anion in ll is typically an anion from a strong inorganic acid, suchas a halide, nitrate, sulfate, etc., but may also be an organic anion,such as the tosylate anion, etc. The anion is advantageously selected soas to increase the solubility of the salt in the electrolysis solvent.E.g., the halides are advantageous when the solvent is water, and atosylate anion is advantageous when an organic solvent is used.

Suitable electrolysis solvents in the subject process are those whicheither dissolve or substantially disperse the sulfonium salt and whichare irreducible or not preferentially electrochemically reduced in theprocess. Suitable solvents are typically polar solvents which includewater, dimethylformamide, hexamethyl phosphoramide, dioxane,acetonitrile, propionitrile, acetic acid, acetic acid-benzene mixtures,lower alkanols, such as methanol, ethanol, isopropanol and butanol; andthe like, and mixtures of such solvents. Most sulfonium salts arereadily soluble in water. Water, therefore, is generally the preferredsolvent. However, in some instances, a solvent which dissolves theproduct is advantageous, such as acetic acid-benzene mixtures.

The concentration of the sulfonium salt in the electrolysis solvent canbe varied from about moles/liter to a saturated solution, but istypically selected at about 0.1 to 1 molar.

The process may be conducted in the presence ofa supporting electrolyte,typically the alkali metal salt of a strong acid, such as KBr, KCl, NaSO NaNO and the like. When used, the supporting electrolyte is added inan amount from about 0.1 to 4 moles/liter. Since the sulfonium salts aregood electrolytes, a supporting electrolyte is generally not required.

The cathode potential (reducing potential) may be maintained at aselected value or may be varied; the only requirement being that thecathode potential is sufficient to reduce the sulfonium salt. Typicalcathode potentials are between about 0.5 and about l.5 volts vs. astandard saturated calomel electrode. The former instance is referred toas controlled-potential electrolysis and is described by L. Meites inTechnique of Organic Chemistry," A. Weissberger-Editor, Vol. 1, 3rd.ed., page 3281, lnterscience, NY. (1959). In the latter instance, thedriving potential (electrical potential between the anode and cathode)is a direct voltage source, such as a battery, and is maintainedconstant while the cathode potential varies to some equilibrium value.The controlled-potential electrolysis system is presently preferred.

In either instance, the cathode is mercury and may suitably be either astirred or unstirred pool of mercury or a dropping mercury electrode. Astirred pool or a dropping mercury cathode is preferred since thecathode surface is constantly being renewed.

It will be important to realize that the choice of cathode potential andreduction rate can influence the yield of the coupled product, e.g.,a,a-dimethylbibenzyl. Very negative cathode settings and low reductionrates favor the formation of ethylbenzene at the expense ofa,a-dimethylbibenzyl.

The method of controlled potential electrolysis as described by Meitesis a convenient way to control the reducing potential at the cathode andby setting this cathode potential at the most positive values consistentwith a reasonable reduction rate the yield of reductively coupledmaterial can be maximized.

Preferably, the electrolyte solution is stirred throughout the processto facilitate movement of the sulfonium ions into the reduction zone. 7

The pH of the electrolyte solution and the temperature are not criticaland may be any value so long as the sulfonium cation is not degraded bythe pH or temperature. Typically, however, the pH is convenientlyselected between about 3 and about 9, and the temperature is betweenabout C. and about 80 C. The higher temperatures increase the reactionrate and allow the reduction to proceed at more positive potentials.

The subject process may be conducted as (a) a batch process or (b) acontinuous process wherein the supply of sulfonium salt is continuouslyrenewed by adding more sulfonium salt per se or by adding ana-methylbenzyl halide which reacts with the sulfide byproduct to formthe sulfonium salt in situ, or by recycling the reaction mixture afterthe product is removed, etc.

The product may be recovered from the reaction mixture by any knownconvenient method, e.g., by solvent extraction or filtration.

SPECIFIC EMBODIMENTS The following examples further illustrate theinvention.

EXAMPLE 1 Preparation of 2,3-Diphenylbutane by Controlled-PotentialElectrolysis A three-compartment glass electrolysis cell as described byL. Meites (see above reference) was used. The cathode compartmentcontained ml. of mercury as the cathode, a magnetic stirring bar, ml.of0.3N tetraethylammonium nitrate (TEAN) in dimethylformamide (DMF) and0.0118 moles of amethylbenzyldimethylsulfonium tosylate (white crystalsm.p. ll0l 13 C.) and was continuously flushed with nitrogen. The centraland anode compartments contained 0.5N TEAN in DMF. The anode was agraphite rod. The cathode potential was maintained at l.0 volts vs. astandard saturated calomel electrode. The process was conducted at roomtemperature. The current ranged from 70 milliamperes (ma.) initially tozero over a period of l 1.5 hours. The product was recovered by removingthe liquid catholyte (DMF) under reduced pressure, washing the resultingsolids with water to remove the TEAN and recrystallizing the remainingsolid in benzene. The white product was identified by infrared and massspectroscopy; yield 64%.

EXAMPLE 2 Preparation of 2,3-Diphenylbutane by Uncontrolled CathodePotential The electrolysis was conducted in a beaker electrolysis cell.A mercury pool was the cathode and a graphite rod was the anode. Enough0.2N a-methylbenzyldimethylsulfonium chloride in water was added tocover the electrodes and an electrical potential (driving voltage) ofabout 3 volts applied; current was 50 ma. A hydrophobic white solidformed at the mercury surface. It was removed and identified as2,3-diphenylbutane by mass spectroscopy.

Similar results are obtained by using substituteda-methylbenzylsulfonium salts as identified above.

We claim:

1. An electrolytic process for preparing compounds having 7 (R). R)n

wherein R is an inert substantially non-interferring halo, hydroxy,nitro or hydrocarbon group or a haloor hydroxysubstituted hydrocarbongroup of from 1 to 25 carbon atoms and n is an integer of from 0 to 5,said process comprising subjecting an a-methylbenzyl sulfonium salt insolution in an elec trolysis solvent to an electrical potentialsufficient to reduce said sulfonium salt at a mercury cathode; saidsulfonium salt having the formula wherein R has the aforesaid meaning,and R and R are alkyl or hydroxy-substituted alkyl groups of from one tocarbon atoms.

2. The process defined in claim 1 wherein R, and R are alkyl orhydroxy-substituted alkyl groups of from one to four carbon atoms.

3. The process defined in claim 1 wherein n is an integer of 5 from O to2.

4. The process defined in claim 3 wherein n is O or I and R is alkyl ora haloor hydroxy-substituted alkyL 5. The process defined in claim 1wherein said electrolysis solvent is water.

6. The process defined in claim I wherein the cathode t i i

2. The process defined in claim 1 wherein R1 and R2 are alkyl orhydroxy-substituted alkyl groups of from one to four carbon atoms. 3.The process defined in claim 1 wherein n is an integer of from 0 to 2.4. The process defined in claim 3 wherein n is 0 or 1 and R is alkyl ora halo- or hydroxy-substituted alkyl.
 5. The process defined in claim 1wherein said electrolysis solvent is water.
 6. The process defined inclaim 1 wherein the cathode potential is maintained at a substantiallyconstant value.
 7. The process defined by claim 4 wherein R1 and R2 areeach alkyl or hydroxy-substituted alkyl groups of from one to fourcarbon atoms.
 8. The process defined by claim 7 wherein n is
 0. 9. Theprocess defined in claim 1 wherein R is a halo, hydroxy or hydrocarbongroup or a halo- or hydroxy-substituted hydrocarbon group.
 10. Theprocess defined in claim 1 wherein the desired product is recovered.